The present invention relates to an apparatus and a method for controlling an internal combustion engine having a variable valve driving system and a variable compression ratio mechanism.
Some of valve driving systems for an internal combustion engine (referred to as an engine hereinafter) are capable of variably controlling the amount of lift of an intake/exhaust valve. Through such control of the intake/exhaust valve, a desired engine output can be generated. On the other hand, a variable compression ratio mechanism for variably controlling a compression ratio in a combustion chamber of an engine has been proposed.
Japanese Patent Application Unexamined Publication (Kokai) No. 2001-263099 discloses a scheme for preventing interference between a piston and an intake valve when a variable compression ratio mechanism for changing a compression ratio by changing the position of the top dead center (TDC) of the piston is used. According to this scheme, under a high compression ratio where the TDC position of the piston becomes high, the timing for opening the intake valve is retarded or a lift amount of the intake valve is decreased.
If an engine output is controlled by the lift amount of the valve, a pumping loss can be decreased and fuel efficiency can be improved. If the compression ratio is controlled based on the operating condition of the engine, the combustion stability can be improved when the engine load is low, and the amount of retarding the ignition timing, which is required for suppressing knocking, can be decreased when the engine load is high.
As the compression ratio increases, the TDC position of the piston approaches the cylinder head. As shown in FIGS. 24(a) and 24(c), when the compression ratio is low, the valve and the piston do not contact each other regardless of the lift amount of the valve because the TDC position of the piston is low. As shown in FIG. 24(b), when the compression ratio is high, the valve and the piston do not contact with each other as long as the lift amount of the valve is small. However, as shown in FIG. 24(d), when the compression ratio is high, the lift amount of the valve may become large, for example, in a transient condition of a valve driving system and/or a compression ratio mechanism. If such a high lift occurs when the compression ratio is high, the valve and the piston may collide with each other. Such a collision may cause damage in the engine.
In order to avoid such a collision, a sufficient amount of “recess” may be provided in the piston. However, if such a recess is provided in the piston, the shape of the upper portion of the piston is complicated, which may cause deterioration in the combustion.
Therefore, there is a need for a control apparatus that is capable of avoiding a collision between a valve and a piston in an engine having a valve driving system that is capable of changing the lift amount of the valve and a variable compression ratio system that is capable of changing the compression ratio.
Furthermore, some of valve driving systems are capable of variably controlling a phase of the valve. In an engine having such a valve driving system and a variable compression ratio mechanism, the following problems may arise. Referring to FIG. 25(a), a reference number 101 indicates the lift amount of a valve and a reference number 102 indicates the position of a piston. When the piston almost reaches TDC, the valve starts to open (at time t1). When the valve opens at a normal phase or at a retarded phase as in this case, the valve and the piston do not collide with each other. However, referring to FIG. 25(b), the phase of the valve is advanced. The valve starts to open before the piston reaches TDC. In this case, the valve and the piston may collide with each other (at time t2).
Therefore, there is a need for a control apparatus that is capable of avoiding a collision between a valve and a piston in an engine further having a valve driving system that is capable of changing a phase of the valve.